The present invention relates to medical devices and methods. More specifically, the invention relates to intervertebral discs and devices and methods for limiting the motion of artificial intervertebral discs.
Back pain takes an enormous toll on the health and productivity of people around the world. According to the American Academy of Orthopedic Surgeons, approximately 80 percent of Americans will experience back pain at some time in their life. In the year 2000, approximately 26 million visits were made to physicians' offices due to back problems in the United States. On any one day, it is estimated that 5% of the working population in America is disabled by back pain.
One common cause of back pain is injury, degeneration and/or dysfunction of one or more intervertebral discs. Intervertebral discs are the soft tissue structures located between each of the thirty-three vertebral bones that make up the vertebral (spinal) column. Essentially, the discs allow the vertebrae to move relative to one another. The vertebral column and discs are vital anatomical structures, in that they form a central axis that supports the head and torso, allow for movement of the back, and protect the spinal cord, which passes through the vertebrae in proximity to the discs.
Discs often become damaged due to wear and tear or acute injury. For example, discs may bulge (herniate), tear, rupture, degenerate or the like. A bulging disc may press against the spinal cord or a nerve exiting the spinal cord, causing “radicular” pain (pain in one or more extremities caused by impingement of a nerve root). Degeneration or other damage to a disc may cause a loss of “disc height,” meaning that the natural space between two vertebrae decreases. Decreased disc height may cause a disc to bulge, facet loads to increase, two vertebrae to rub together in an unnatural way and/or increased pressure on certain parts of the vertebrae and/or nerve roots, thus causing pain. In general, chronic and acute damage to intervertebral discs is a common source of back related pain and loss of mobility.
When one or more damaged intervertebral discs cause a patient pain and discomfort, surgery is often required. Traditionally, surgical procedures for treating intervertebral discs have involved discectomy (partial or total removal of a disc), with or without interbody fusion of the two vertebrae adjacent to the disc. When the disc is partially or completely removed, it is necessary to replace the excised material to prevent direct contact between hard bony surfaces of adjacent vertebrae. Oftentimes, pins, rods, screws, cages and/or the like are inserted between the vertebrae to act as support structures to hold the vertebrae and graft material in place while they permanently fuse together. One typical fusion procedure is achieved by inserting a “cage” that maintains the space usually occupied by the disc to prevent the vertebrae from collapsing and impinging the nerve roots. The cage is used in combination with bone graft material (either autograft or allograft) such that the two vertebrae and the graft material will grow together over time, forming bridging bone between the two vertebrae. The fusion process typically takes 6-12 months after surgery. During this time external bracing (orthotics) may be required. External factors such as smoking, osteoporosis, certain medications, and heavy activity can prolong or even prevent the fusion process. If fusion does not occur, patients may require reoperation. It would be desirable to achieve immobilization of the vertebrae and maintain spacing between the adjacent vertebrae without the associated patient discomfort and long recovery time of traditional interbody fusion.
In an attempt to treat disc related pain without fusion provided by bridging bone, an alternative approach has been developed, in which a movable, implantable, artificial intervertebral disc (or “disc prosthesis”) is inserted between two vertebrae. A number of different artificial intervertebral discs are currently being developed. For example, U.S. Patent Application Publication Nos. 2005/0021146, 2005/0021145, and 2006/0025862, which are hereby incorporated by reference in their entirety, describe artificial intervertebral discs. Other examples of intervertebral disc prostheses are the LINK SB CHARITÉ™ disc prosthesis (provided by DePuy Spine, Inc.) MOBIDISK™ disc prosthesis (provided by LDR Medical), the BRYAN™ cervical disc prosthesis (provided by Medtronic Sofamor Danek, Inc.), the PRODISC™ disc prosthesis or PRODISC-C™ disc prosthesis (from Synthes, Inc.), the PCM™ disc prosthesis (provided by Cervitech, Inc.), and the Maverick® disc (provided by Medtronic Sofamor Danek).
Although artificial discs provide a tremendous advantage over fusion in allowing the vertebrae to articulate after removal of the natural disc, sometimes an artificial disc does not provided the desired pain relief. In many cases where pain relief is not achieved, the artificial disc is removed and the patient then gets a traditional fusion. Removal of the disc is a difficult process generally involving anterior access to the spinal column through the abdominal cavity and removal of the disc often with additional bone. This procedure is complicated by the scar tissue which is present from the original surgery.
Accordingly, it would be desirable to have a device capable of limiting the motion of an artificial disc in a subsequent operation without needing to remove the entire disc. It would also be advantageous to provide a device capable of limiting motion of the disc which is inserted posteriorly.
In addition, although the existing artificial discs provide advantages over traditional fusion methods, many patients are not candidates for an artificial disc due to facet degeneration, instability, poor bone strength, previous surgery, multi-level disease, and pain sources that are non-discogenic. However, if there was a relatively easy way to convert an artificial disc to a fusion post operatively surgeons might be more willing to try the new artificial discs in patients which are on the borderline between being candidates for an artificial disc and a fusion.
Therefore, a need exists for an improved artificial disc or an insert for an artificial disc which can relatively easily convert an artificial disc to a more rigid fusion like device by the post operative addition of an insert.